contrib/openocd.udev: fix warning

contrib/openocd.udev: fix warning

Fix following warning message logged by udev at start

udevd[421]: SYSFS{}= will be removed in a future udev
version, please use ATTR{}= to match the event device,
or ATTRS{}= to match a parent device, in
/etc/udev/rules.d/95-openocd.rules:81

Change-Id: I6de935c13a3327e3d718c110f97d19b9847ceca5
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/552
Tested-by: jenkins
Reviewed-by: Luca Bruno
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>